Mayhem firmware

Revision (v1.4.0):

• Updated HackRF submodule to greatscottgadgets/hackrf@5f1536c dfa1a98
• Recognition of audio chip 838451f #327 (comment) (thanks @zhang00963)
• AM/SSB/DSB Microphone Functionality #329 (thanks @aldude999)
• Add APRS Receiving App f15cf78 (thanks @East2West)
• New GSM-FR.TXT file for sdcard/FREQMAN 5948907 (thanks @RedFox-Fr)
• More snap values to the calls app d60299a (thanks @fossum)
• Fix bug on radiosonde Meteoman Lat & lon calculation 50bab79 (thanks @euquiq)
• Added Pocsag bitrate 62c1e4e (thanks @ImDroided)
• Big cleanup of warnings in the compilation process (thanks @GullCode)